The present invention relates to vehicle trailer hitch adapters, and more particularly to adapters that provide vertically variable offset mounting of trailer hitches relative to fixed hitch mounting structure of towing vehicles.
Traditionally, the towing of a trailer (or towed vehicle) by a towing vehicle such as an automobile involves fixably mounting of a hitch ball to a supporting structure of the towing vehicle, such as to a rear bumper of the vehicle. Conventional hitch balls have an approximately spherical head portion, a flange portion with a threaded stem, and a neck portion spacing the head portion above the flange portion. A typical mounting, such as is presently found on some light pick-up trucks, includes a hole formed in a shelf portion of the rear bumper for receiving the stem, which is fastened by a nut that threadingly engages the stem. Other mountings include an adapter having a projecting tab member counterpart of the bumper shelf portion that is clamped to a conventional rear bumper (and which may incorporate means for selective vertical offset of the tab member); and a hitch mount that fixably supports the tab member to a chassis frame of the vehicle, either by bolting, clamping, or welding. In recent times so-called xe2x80x9cmodularxe2x80x9d hitches have become common, wherein a longitudinally extending rectangular socket is formed in the hitch mount for receiving a tubular hitch shank. A hole can be formed in a rearwardly projecting portion of the shank itself for receiving the stem of the ball (the rearwardly projecting portion forming a counterpart of the tab member), but more commonly a counterpart of the tab member is welded to the shank in offset relation thereto. The shank is fixedly retained in the socket by a clevis pin or bolt fastener that engages aligned transverse openings of the shank and the socket. As used below, the term xe2x80x9cmodular hitchxe2x80x9d means the shank and tab member, being typically provided in a variety of vertical offsets from which selection is made for matching the mounted height of the a ball to a desired height of a trailer hitch to be coupled thereto.
In practice it has been found advantageous to provide for vertical adjustment of the trailer hitch ball relative to the towing vehicle chassis without having to replace the modular hitch. This avoids the need for a correct a priori offset selection, and/or for exchanging the modular hitch to accommodate different towed vehicles and/or different loadings of the towed and/or towing vehicle. See, for example, U.S. Pat. No. 4,033,601 to Lindahl et al., and U.S. Pat. No. 4,429,895 to Hunter. Further, it is advantageous to be able to adjust the vertical offset while the towed vehicle is already coupled to the ball and both vehicles are loaded. U.S. Pat. No. 4,103,928 to Sheppard, Jr., discloses such a device, including a mounting plate for vertically oriented attachment to the trailer hitch of the towing vehicle, a slide plate moveable up and down with respect to the mounting plate by means of a jack screw, and a tongue projecting rearwardly from the slide plate for receiving the ball. The slide plate is confined between the mounting plate and a pair of laterally spaced face plates that overhang inwardly from a pair of spacer plates, the jack screw being supported by a thrust bearing that is received in a top plate that is mounted at upper extremities of the face plates, spacer plates, and the mounting plate, an upper extremity of the jack screw is formed to receive a wrench or other device by which the screw is turned, and a locking device selectively engages the upper extremity to secure the screw against rotation. A traveler nut that engages the jack screw is captured at an upper extremity of a box structure that is fixed on the slide plate. Also, several set screws are threaded through the face plates for clamping the slide plate.
The adjustable hitch of Sheppard, Jr., has a number of disadvantages. For example:
1. The jack screw, thrust bearing, and traveler nut are subject to excessive wear and premature failure in that the arrangement of set screws is believed to be ineffective for preventing shock loading of the jack screw during towing;
2. The arrangement of set screws is awkward to use in that only some of the set screws are located for clamping the slide plate at any particular vertical position thereof, those not clamping the slide plate being loose and subject to falling out unless they are tightened in a way that blocks subsequent adjustment of the slide plate;
3. The hitch is excessively bulky in relation to the range of adjustment provided, in that the slide plate cannot be raised above the tops of the face plates, being blocked by the top plate, and the vertical height of engagement of the slide plate is diminished to the extent that the slide plate projects below the mounting, spacer, and face plates;
4. The hitch provides an excessively limited amount of ground clearance in relation to elevated positions of the tongue as a consequence of the above disadvantage, particularly when a range of adjustment of the tongue to proximate ground level is required;
5. The hitch is awkward to use in that a separate device is required for turning the jack screw, which device must be removed during locking and unlocking of the jack screw; and
6. The hitch is excessively difficult to maintain in that exposed sliding surfaces of the face plates, spacer plate, and mounting plate are relatively inaccessible for cleaning.
Thus there is a need for an adjustable trailer hitch apparatus that overcomes the disadvantages of the prior art.
The present invention meets this need by providing a trailer hitch apparatus with a wide range of vertical adjustment down to proximate ground level, yet has generous ground clearance in its raised positions, using an elevator mechanism that is not subject to shock loading during towing. In one aspect of the invention, the apparatus includes a base member adapted for fixable mounting onto the towed vehicle; a guide unit rigidly connected to a rear extremity of the base member and defining a vertically oriented guide surface when the base member is mounted onto the towing vehicle; a track unit defining a track surface engaging the guide surface for axially guided movement relative thereto; means on the track unit for connecting a coupling receiver; an elevator mechanism connected between the guide unit and the track unit for raising and lowering the track unit; and a lock mechanism for positively locking the track member in a selectable one of a plurality of axially spaced positions relative to the guide unit.
The guide surface can include a plurality of guide surface portions, each of the guide surface portions being generally inwardly facing relative to others of the guide surface portions, the track surface including a corresponding plurality of generally outwardly facing track surface portions. The track surface can extend fully between opposite end extremities of the guide surface over a full range of travel of the track member. The guide surface can include a rearwardly facing guide surface portion, a spaced pair of forwardly facing guide surface portions, and a laterally spaced pair of inwardly facing guide surface portions. The guide unit can include a guide plate defining the rearwardly facing guide surface portion, and a pair of guide members, the guide members each being fixably connected to the guide plate and defining respective ones of the forwardly facing and inwardly facing guide surface portions.
The track unit can include a column member and a laterally spaced pair of track members fixedly connected to the column member, the track surface being formed on the track members. Each of the track members can define a forwardly facing first track surface, a rearwardly facing second track surface disposed rearwardly of the first track surface, and a laterally outwardly facing third track surface.
The elevator mechanism can include a jackscrew journaled proximate an upper extremity of the track unit and having threaded engagement with the guide unit proximate an upper extremity thereof. The hitch apparatus can further include a crank for manually turning the jackscrew. The crank can be connected to an upper extremity of the jackscrew.
The lock mechanism can include a registration member fixably mounted on the guide unit and having a transverse lock passage formed therein, the track unit having an axially spaced plurality of lock openings formed therein for selective alignment with the lock passage during operation of the elevator mechanism, and a lock pin for engaging the lock passage and the selected one of the lock openings. The lock passage can be one of a vertically spaced plurality of lock passages wherein at least one spacing of the lock passages is different than a spacing of the lock openings for selectable locking of the track unit at position spacings being less than an axial spacing of the lock openings.
The means for connecting can include a rearwardly facing first socket member for receiving a modular trailer hitch, the first socket member being fixedly located proximate a lower extremity of the track member and having an opening formed in opposite walls thereof for receiving a hitch retainer pin by which to secure the trailer hitch in fixed engagement with the first socket member. The hitch apparatus can include a hitch stem member of the modular trailer hitch, the hitch stem member being configured for mounting a hitch ball and having a hitch shank portion being insertable into the first socket member, the hitch shank portion having a transverse passage for receiving the hitch retainer pin. The hitch apparatus can further include a hitch ball of the modular trailer hitch, the hitch ball being mountable onto the stem member opposite the shank portion thereof. The means for connecting can further include a rearward facing second socket member counterpart of the first socket member, the second socket member being spaced above the first socket member. The second socket member can be located proximate an upper extremity of the track member. The means for connecting can further include a rearward facing third socket member counterpart of the first socket member, the third socket member being spaced between the first and second socket members.
The base member-can include a forwardly projecting base stem member having a base shank portion for insertion into a rearwardly opening hitch socket of the towing vehicle, the base stem having a transverse base retainer passage for receiving a hitch retainer pin when the retainer pin also engages a retainer opening of the hitch socket. The base retainer passage can be one of a longitudinally spaced plurality of base retainer passages for longitudinally selective mounting of the apparatus onto the towed vehicle.